The present invention is directed to an internal combustion engine, particularly, to a four cycle radial internal combustion engine for use in the aircraft, automotive, marine and industrial fields.
The four-stroke internal combustion engine with its inherent reliability and fuel economy is well known. It has been used in various products, ranging from lawn mower engines to automobiles. Such engines, however, are hampered by low power-to-weight ratio which is inherent in four-stroke engines.
U.S. Pat. No. 1,962,530 and U.S. Pat. No. 1,967,596, both issued to J. Schubert, exemplify the state of the prior art relating to two cycle internal combustion radial engines. As noted by Schubert, many attempts have been made to produce a practical two cycle engine suitable for aircraft or other power plants to replace the typically heavy, complex and expensive four cycle engine which was in general use. Some of the essential factors considered by Schubert in the design of his two cycle engine were proper lubrication, cooling, fuel distribution, high volumetric and thermal efficiency, speed and low weight per horsepower. The two cycle engine however is very noisy, producing what has been referred to as a maniacal whine, and is not as smooth running as the four cycle engine.
It is therefore an object of the present invention to provide a highly efficient low weight four cycle engine in the 45 to 65 horsepower range. The four cycle radial engine of the present disclosure combines the advantages of both the four cycle and the two cycle engines heretofore known in the prior art. The radial engine of the present disclosure runs with the smoothness one would expect from a four-stroke engine, yet it is light weight, quiet and fuel efficient. The compact nature of the radial engine of the present disclosure results in a very low weight displacement ratio and consequently a satisfactory power-to-weight ratio. There are two rows of three cylinders each, for a total of six cylinders. This arrangement gives a firing impulse every 120 degrees, or three power impulses per revolution. Each of the two three-cylinder rows forms a system whose instantaneous mass center or centroid has an approximately circular locus that is exactly balanced by the equal and opposite mass system of the other cylinder row. That is, one cylinder row is in static balance with the other cylinder row. The measured dry weight of the radial engine of the present disclosure is less than 84 pounds. Each of the six cylinders is therefore required to produce only eleven horsepower to produce the desired horsepower range for powering a small aircraft. Each cylinder is individually exposed to its own flow of cooling air without the requirement for extensive baffling and ducting. The low per-cylinder horsepower output provides an additional cooling advantage making cooling demands for this engine very manageable.